Lesson Plan - Get It!
Is it possible to break or crack the rock pictured above without touching it?
Rock, minerals, and soil are not stationary or unchanging objects.
While they are incapable of moving or changing themselves, they are frequently moved and changed by people and natural forces. The process of breaking down and moving rock, mineral, and soil is called weathering, erosion, and deposition.
In this lesson, you will learn about weathering.
Weathering is the process of breaking down or changing rock, minerals, and soil. There are two types of weathering: physical and chemical.
Physical weathering is also referred to as mechanical weathering. Physical weathering occurs when rocks are broken into smaller pieces. After physical weathering you end up with the same thing you started with, but in smaller chunks.
Chemical weathering is similar to physical weathering in that you start with something big and end with something smaller. However, with chemical weathering, the thing you end up with is not just a smaller version of the thing you started with. It's a different thing altogether.
Let's do a demonstration to make this difference a little clearer.
- Are you ready for a snack?
Get some crackers (saltines or graham crackers). Cough drops or hard candies (like a peppermint) can be substituted. Anything that will dissolve in your mouth will work.
Now, chew the first cracker (or candy). Be careful not to hurt your teeth!
Your teeth are breaking apart the food. You may have started with a cracker, but your teeth turned it into smaller pieces of cracker.
Take another cracker (or candy). Put it in your mouth; but this time, try not to chew it.
- You should still feel the cracker getting smaller, but how?
You have probably figured out that your saliva is what's causing the food to get smaller. Your saliva is slightly acidic, which causes the chemical bonds in the food to break apart.
I know what you're thinking - what this lesson needs is an auto-tuned Ed Sheeran cover about weathering. Well, good news! You're in luck.
Watch ParrMr's Weathering and Erosion Song. Learn it, then sing it for all of your friends!
Physical weathering can be caused by several different things. First, when there are droughts or long periods of time without rain, rocks and soil can dry out and crack. During rainy seasons, water can become trapped inside the cracks in rocks and soil. If this water freezes, the frozen water, or ice, expands. As it does, it causes the rock or soil to break.
To examine pictures of physical weathering, visit The Geological Society of London's web page, Physical Weathering.
Chemical weathering affects the atomic makeup of the rock or soil. Acid rain is acidic precipitation that is created by pollution in the atmosphere. Acidic material contains a lot of hydrogen ions. These excess hydrogen ions can cause chemical reactions, such as burns, rust, and corrosion. Lemons and limes are both acidic. This is why they taste sour. Acid rain can cause a chemical reaction to occur in rocks and soil, changing them into something else.
(If you are unsure what is meant by atomic structure, review the Elephango lesson found in the right-hand sidebar under Additional Resources.)
To learn about other types of chemical weathering, check out The Geological Society of London's Chemical Weathering page.
For a quick review, watch Michael DiPasquale explain Types of Weathering in this video:
Now that you know what weathering is and the different types of weathering, move on to the Got It? section to assess what you have learned.